U.S. patent application number 10/372973 was filed with the patent office on 2004-08-26 for method for increasing the beta of pnp bjt device in cmos process.
This patent application is currently assigned to UNITED MICROELECTRONICS CORP. Invention is credited to Lee, Tong-Hsin.
Application Number | 20040166625 10/372973 |
Document ID | / |
Family ID | 32868620 |
Filed Date | 2004-08-26 |
United States Patent
Application |
20040166625 |
Kind Code |
A1 |
Lee, Tong-Hsin |
August 26, 2004 |
Method for increasing the Beta of PNP BJT device in CMOS
process
Abstract
A method for improving the Beta (.beta.) of a parasitic PNP
bipolar junction transistor (BJT) in a conventional CMOS process
includes the steps of: providing a P-type substrate having a
shallow region corresponding to the P.sup.+ electrode of the
parasitic PNP BJT and the P.sup.+ electrode is located within and
in contact with an N-well; forming an electrostatic discharge (ESD)
mask layer on the P-type substrate, wherein the mask layer has a
pattern exposing an area corresponding to the P.sup.+ electrode of
the PNP parasitic BJT, and exposing one electrode of an ESD device;
and implanting P.sup.+ ions to the P-type substrate, thereby
deepening a P/N junction of the P.sup.+ electrode of the parasitic
BJT and the N-well.
Inventors: |
Lee, Tong-Hsin; (Taipei
Hsien, TW) |
Correspondence
Address: |
ARENT FOR KINTNER PLOTKIN & KAHN, PLLC
Suite 400
1050 Connecticut Avenue, N.W.
Washington
DC
20036-5339
US
|
Assignee: |
UNITED MICROELECTRONICS
CORP
|
Family ID: |
32868620 |
Appl. No.: |
10/372973 |
Filed: |
February 26, 2003 |
Current U.S.
Class: |
438/231 ;
257/E21.642; 257/E27.063; 438/202 |
Current CPC
Class: |
H01L 21/823878 20130101;
H01L 27/0921 20130101 |
Class at
Publication: |
438/231 ;
438/202 |
International
Class: |
H01L 021/8238 |
Claims
What is claimed is:
1. A method for increasing the Beta (.beta.) of a parasitic bipolar
junction transistor (BJT) in a CMOS, said method comprising:
providing a substrate having an area corresponding to a first
electrode of a parasitic BJT, a second electrode of said parasitic
BJT being in contact between said first electrode and a third
electrode of said parasitic BJT; forming a mask layer on said
substrate, wherein said mask layer has a pattern exposing an area
corresponding to said first electrode of said parasitic BJT; and
implanting ions to said substrate, wherein implanted ions have the
same conductivity type as said first electrode of said parasitic
BJT, thereby deepening a junction of said first electrode and said
second electrode of said parasitic BJT.
2. The method according to clam 1, further comprising another area,
within said substrate, which corresponds to one electrode of an
electrostatic discharge (ESD) device.
3. The method according to claim 2, wherein said ions are also
implanted into said area corresponding to said electrode of said
ESD device, thereby forming another electrode of said ESD device,
resulting in said ESD device.
4. The method according to claim 3, wherein said mask layer is an
ESD mask layer used in an ESD process.
5. The method according to claim 1, wherein said mask layer
comprises photoresist.
6. The method according to claim 1, wherein said implanted ions
comprises boron (B).
7. The method according to claim 1, wherein said implanted ions
have concentration of about 1E13.about.1E14 atoms/cm.sup.2.
8. The method according to claim 1, wherein said ions are implanted
with energy of about 30.about.50 KeV.
9. A method for increasing the Beta (.beta.) of a parasitic PNP
bipolar junction transistor (BJT) in a CMOS, said method
comprising: providing a P-type substrate, wherein said P-type
substrate includes a shallow region corresponding to a P.sup.+
electrode of a parasitic PNP BJT, said P.sup.+ electrode is located
within and in contact with an N-well, thereby said P.sup.+
electrode, said N-well, and said P-type substrate forming said
parasitic PNP BJT; forming an electrostatic discharge (ESD) mask
layer on said P-type substrate, wherein said mask layer has a
pattern exposing an area corresponding to said P.sup.+ electrode of
said PNP parasitic BJT, and exposing one electrode of an ESD
device; and implanting P.sup.+ ions to said P-type substrate,
thereby deepening a P/N junction of said P.sup.+ electrode of said
parasitic BJT and said N-well.
10. The method according to claim 9, wherein said ions are also
implanted into said one electrode of said ESD device, thereby
forming another electrode of said ESD device, resulting in said ESD
device.
11. The method according to claim 9, wherein said ESD mask layer
comprises photoresist.
12. The method according to claim 9, wherein said implanted ions
comprise boron (B).
13. The method according to claim 9, wherein said implanted ions
have concentration of about 1E13.about.1E14 atoms/cm.sup.2.
14. The method according to claim 9, wherein said ions are
implanted with energy of about 30.about.50 KeV.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention generally relates to the field of improving
the Beta (.beta.) of a parasitic PNP bipolar junction transistor
(BJT) in a complementary metal oxide semiconductor (CMOS) process.
More particularly, the present invention relates to a method to
deepen the P'/N-well junction depth of the parasitic PNP BJT in an
electrostatic discharge (ESD) implanting process.
[0003] 2. Description of the Prior Art
[0004] The parasitic PNP BJT has commonly been used in a bandgap
voltage circuit for a conventional CMOS process, and using the CMOS
process to make the bandgap voltage circuit benefits from the cost
of savings more than by using a precision-trimmed bipolar process
does. However, the .beta. of the parasitic PNP BJT is normally
poorer than a preferred one due to the compatibility of the CMOS
process, and it is inversely proportional to the base width, which
is controlled by N-well doping concentration and P.sup.+/N-well
junction depth.
[0005] Hence, there are two ways for improving the .beta. of the
parasitic PNP BJT in the conventional CMOS process: one is to dope
lighter concentration into the N-well; the other one is to make the
P.sup.+/N-well junction deeper. Nevertheless, these two ways can
respectively cause a poorer P.sup.+/P-well isolation and a poor
device roll-off characteristic although the .beta. of the parasitic
PNP BJT is improved in the CMOS process.
[0006] According to the conventional CMOS process, particularly,
making the P.sup.+/N-well junction of the parasitic PNP BJT deeper
to improve the .beta. in a normal P.sup.+ junction implanting
process can result in all transistors, not only the parasitic PNP
BJT, on the wafer having deeper junctions, and this situation
causes a short channel effect and a poor device roll-off
characteristic. Otherwise, making the P.sup.+/N-well junction of
the parasitic PNP BJT deeper after the normal P.sup.+ junction
implanting process needs additional masks and processes, and this
procedure can make extra costs compared to the conventional CMOS
process.
[0007] As shown in FIG. 1, after a normal P.sup.+ junction
implanting process, a P-type substrate 100 includes spaced-apart
N.sup.+ regions 110 and 120, a channel region (not numbered)
between the spaced-apart N.sup.+ regions 110 and 120, shallow
trench isolation (STI) structures 1501 and 1502 contiguous with the
spaced-apart N.sup.+ regions 110 and 120, respectively, and a gate
structure 160 positioned over the channel region. The P-type
substrate 100 also includes an N-well region 1302 and a P.sup.+
region 1301 within and in contact with the N-well region 1302 to
form a P.sup.+/N-well junction, and a STI structure 1503 contiguous
with the P.sup.+/N-well junction. Wherein, the P.sup.+ region 1301,
the N-well region 1302, and the P-type substrate 100 form a
parasitic PNP BJT.
[0008] As shown in FIG. 2, an ESD implanting process is used to
decrease the N.sup.+/P-well junction breakdown voltage. The
dopants, boron (B) at a dose of 1E13.about.1E14 atoms/cm.sup.2, are
directly implanted into the spaced-apart N.sup.+ regions 110 and
120 at an energy of 30.about.50 KeV. However, the region 130 of the
P.sup.+/N-well junction of the parasitic PNP BJT cannot benefit
from the ESD implanting process since the region 130 is covered by
photoresist 140.
[0009] As shown in FIG. 3, after the ESD implanting process, ESD
devices 1101 and 1201 are formed under the spaced-apart N.sup.+
regions 110 and 120, respectively. By doing so, the N.sup.+/P-well
junction breakdown voltage can be decreased. The junction depth of
the P.sup.+ region 1301 and the N-well region 1302 has no change
after the ESD implanting process and still retains at the same
depth as before, and hence the .beta. of the parasitic PNP BJT is
still poor.
[0010] In view of the drawbacks mentioned with the prior art
process, there is a continued need to develop new and improved
processes that overcome the disadvantages associated with prior art
processes. The advantages of this invention are that it solves the
problems mentioned above.
SUMMARY OF THE INVENTION
[0011] In accordance with the present invention, a method to
improve the .beta. of the parasitic PNP BJT in the conventional
CMOS process substantially obviates one or more of the problems
resulted from the limitations and disadvantages of the prior art
mentioned in the background.
[0012] Accordingly, one object of the present invention is to
provide a method for improving the .beta. of the parasitic PNP BJT
in the conventional CMOS process without additional masks and
processes.
[0013] Another object is to provide a method for improving the
.beta. of the parasitic PNP BJT in the conventional CMOS process by
deepening the P.sup.+/N-well junction of the parasitic PNP BJT in
the ESD implanting process.
[0014] Still another object is to provide a method for improving
the .beta. of the parasitic PNP BJT in the conventional CMOS
process without any side effects on other normal P.sup.+
junctions.
[0015] According to the objects mentioned above, the present
invention provides a method for improving the .beta. of the
parasitic PNP BJT in the conventional CMOS process, including:
forming an exposing area by using an ESD mask with an extra
exposing area corresponding to the P.sup.+/N-well junction of the
parasitic PNP BJT; performing an ESD implanting process on both
forming ESD devices and deepening the P.sup.+/N-well junction.
Herein, the ESD mask can be used in patterning the exposing areas
for the ESD devices and the P.sup.+/N-well junction at the same
time. Hence, the dopants, boron (B) at a dose of 1E13.about.1E14
atoms/cm.sup.2, can be implanted into not only the spaced-apart
N.sup.+ regions to form the ESD devices but also the parasitic PNP
BJT to deepen the P.sup.+/N-well junction in the ESD implanting
process. This is, the extra ESD implanting process to the parasitic
PNP BJT results in a deeper P.sup.+/N-well junction and a higher
.beta. without any side effect on other normal P.sup.+ junctions.
In other words, the method uses the adjusted masks and the same
process steps without any additional masks and processes compared
to a conventional CMOS process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated as the same
becomes better understood with reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
[0017] FIG. 1 shows cross-sectional views of a parasitic PNP BJT in
a CMOS after a normal P.sup.+ implanting process;
[0018] FIG. 2 and FIG. 3 show cross-sectional views of the
parasitic PNP BJT in the CMOS in an ESD implanting process and
after the ESD implanting process, respectively;
[0019] FIG. 4 shows cross-sectional views of a parasitic PNP BJT in
a CMOS after a normal P.sup.+ implanting process;
[0020] FIG. 5 shows cross-sectional views of the parasitic PNP BJT
in the CMOS in an ESD implanting process in accordance with the
present invention; and
[0021] FIG. 6 shows cross-sectional views of the improved parasitic
PNP BJT in the CMOS in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] Some embodiments of the invention will now be described in
greater detail. Nevertheless, it should be noted that the present
invention can be practiced in a wide range of other embodiments
besides those explicitly described, and the scope of the present
invention is expressly not limited except as specified in the
accompanying claims.
[0023] Moreover, it should be noted that the drawings are in
greatly simplified form and they are not drawn to scale and
dimensions have been exaggerated in order to provide a clear
illustration and understanding of the present invention.
[0024] In accordance with the present invention, a method is
provided for improving the .beta. of the parasitic BJT in the
conventional CMOS process without any extra masks, processes, and
side effects on normal junctions, including the steps of: providing
a substrate having an area corresponding to a first electrode of a
parasitic BJT, a second electrode of the parasitic BJT being in
contact between the first electrode and a third electrode of the
parasitic BJT, and another areas corresponding to the electrodes of
ESD devices; forming a mask layer on the substrate, wherein the
mask layer including photoresist has a pattern exposing areas
corresponding to the first electrode of the parasitic BJT and to
the electrodes of the ESD devices; and implanting ions to the
substrate, wherein implanted ions have the same conductivity type
as the first electrode of the parasitic BJT, having concentration
of about 1E13.about.1E14 atoms/cm.sup.2, and are implanted with an
energy of about 30.about.50 KeV, thereby deepening a junction of
the first electrode and the second electrode of the parasitic BJT
and forming the ESD devices.
[0025] As shown in FIG. 4, after a normal P.sup.+ junction
implanting process, a P-type substrate 200 includes spaced-apart
N.sup.+ regions 210 and 220, a channel region (not numbered)
between the spaced-apart N.sup.+ regions 210 and 220, shallow
trench isolation (STI) structures 2501 and 2502 contiguous with the
spaced-apart N.sup.+ regions 210 and 220, respectively, and a gate
structure 260 positioned over the channel region. The P-type
substrate 200 also includes an N-well region 2302 and a P.sup.+
region 2301 within and in contact with the N-well region 2302 to
form a P.sup.+/N-well junction, and a STI structure 2503 contiguous
with the P.sup.+/N-well junction. Wherein, the P.sup.+ region 2301,
the N-well region 2302, and the P-type substrate 200 form a
parasitic PNP BJT.
[0026] As shown in FIG. 5, an ESD mask layer including photoresist
(cannot be seen in FIG. 5 since the areas in FIG. 5 need to be
exposed) is formed on the P-type substrate. Furthermore, the ESD
mask layer has a pattern exposing the areas corresponding to the
P.sup.+ region 2301 of the PNP parasitic BJT and to the electrodes
210 and 220 of ESD devices. Implanted ions, boron (B) at a dose of
1E13.about.1E14 atoms/cm.sup.2, are directly implanted into the
spaced-apart N.sup.+ regions 210 and 220 as well as the region 230
of the P.sup.+/N-well junction of the parasitic PNP BJT at an
energy of 30.about.50 KeV.
[0027] As shown in FIG. 6, after the ESD implanting process, the
ESD devices 2101 and 2201 are formed under the spaced-apart N.sup.+
regions 210 and 220, respectively. By doing so, the N.sup.+/P-well
junction breakdown voltage can be decreased. Moreover, the junction
depth of the P.sup.+ region 2301 becomes deeper (2301 and 23011).
Hence, the .beta. of the parasitic PNP BJT is improved by deepening
the P.sup.+/N-well junction depth. Further, there are no side
effects, for example, a short channel effect, on a normal P'
junction since the implanted ions are only implanted into the ESD
devices regions and the parasitic PNP BJT region.
[0028] The method in accordance with the present invention uses the
same processes and masks without any extra cost compared to the
conventional CMOS process. A key issue for the method is to adjust
an extra exposing area corresponding to the parasitic PNP BJT on
the ESD mask so that the photoresist can be patterned and removed
to form an exposing area on the parasitic PNP BJT during the ESD
implanting process. As to the other process steps are the same as
those in the convention CMOS process.
[0029] However, it is to be understood and appreciated that the
process steps and structures described above do not cover a
complete process flow. The present invention can be practiced in
conjunction with various fabrication techniques that are used in
the art, and only so much of the commonly practiced process steps
are included herein as are necessary to provide an understanding of
the present invention.
[0030] Although specific embodiments have been illustrated and
described, it will be obvious to those skilled in the art that
various modifications may be made without departing from what is
intended to be limited solely by the appended claims.
* * * * *